The invention relates to a thin-walled, sheet-like component of high strength comprising hydraulically cured concrete and to a process for producing it.
Cured mortars reinforced with steel fiber mats are known under the name xe2x80x9cslurry infiltrated mat concretexe2x80x9d, hereinafter also referred to as SIMCON. Such concrete is produced by firstly preparing a flowable mortar from portland cement, water, sand, microsilica and superfluidizer and, for example, pouring it into a mold in which a steel fiber mat is located, so that the steel fiber mat is impregnated with mortar. Curing results in a concrete reinforced with steel fibers which has a considerably higher ductility and a more favorable crack distribution which gives higher strength on overloading compared to an unreinforced concrete. SIMCON is used to produce, for example, covering layers on components or lost shuttering (ACI Structural Journal/September-October 1997, pp. 502-512). However, only relatively thick and flat components having a minimum thickness of, for example, from 15 to 20 mm can be produced from SIMCON because the steel fiber mats are relatively thick and complete incorporation of the mats with flowable fresh mortar is relatively difficult.
It is an object of the invention to provide thin-walled components of high elasticity, in particular in respect of elastic bending, and high performance on the basis of cured concrete reinforced with steel fiber mats and also to provide a process for producing it by means of which not only thin-walled, flat components but also thin components having any curved or angled shapes can be produced.
These objects are achieved by the features of claims 1 and 24. Advantageous embodiments of the invention are defined in the subordinate claims dependent on these main claims.
The invention provides for the use of commercial, compressed mats of steel wool. Preference is given to using stainless steel wool mats which have a higher strength and a very low oxidation rate and therefore have long-term corrosion resistance in the presence of, for example, water and/or moisture.
The stainless steel wool is, for example, produced from the material No. DIN 1.4113 or 1.4793 or from stainless alloy steels. Different mats have fibers of different fineness; for example, a mat having a mean fiber diameter of 0.08 mm is chosen for components having a thickness of xe2x89xa65 mm, while coarser, medium fiber diameters of, for example, 0.12 mm are suitable for components having a greater thickness. The fiber lengths are in the range from about 20 mm to a number of meters; their average length is a number of decimeters.
This long-fiber stainless steel wool is elastic and tough. The fibers have length/diameter ratios (L/D ratios) of over 1000. Accordingly, this ratio is far above the critical value at which an increase in fiber lengths still has a property-improving effect.
The mats are very flexible and bendable, have a width of up to 1 m and are available in weights per unit area of, for example, from 800 g/m2 to 2000 g/m2 rolled up into rolls. The mats can be cut with shears.
For the purposes of the invention, preference is given to using stainless steel wool having a weight per unit area of from 900 to 1000 g/m2 and a mean fiber diameter of from 0.08 to 0.12 mm.
In combination with the selected and compressed steel wool mat product in the form of steel wool fibers, in particular stainless steel wool, use is made of a suspension based on superfine cement.
Superfine cements are very fine hydraulic binders which are characterized by their chemomineralogical composition and a continuous and gradated particle size distribution. They generally comprise the customary cement raw materials such as milled portland cement clinker and/or milled slag sand and setting regulators; they are produced in separate production plants in cement works. The individual milling of the mineral starting materials, separation of their very fine constituents and their targeted composition in respect of, inter alia, particle sizes and particle size distribution are particularly advantageous.
The important feature of superfine cements which distinguishes them from conventional standard cements, e.g. in accordance with DIN 1164, is the comparatively great fineness of these binders together with the limitation of their largest particles, which is usually indicated by reporting of the particle diameter at 95% by mass of the mixture, namely d95.
Preference is given to using superfine cements based on slag sand or portland cement having a continuous and gradated particle size distribution having a d95xe2x89xa624 xcexcm, preferably xe2x89xa616 xcexcm, and a mean particle size d50 of xe2x89xa67 xcexcm, preferably xe2x89xa65 xcexcm. These are converted into suspensions by mixing them with water and with at least one superfluidizer (these are highly effective fluidizers or flow improvers) and also, in particular, with microsilica. and/or pigments and/or inert mineral materials, e.g. ground limestone and/or quartz flour and/or fly ash, of the same or lower fineness as the superfine cement.
Microsilicas are products which are obtained in the processing of ferrosilicon. They are generally used in the form of aqueous dispersions as additives in high-performance concrete. This type of microsilica is known as xe2x80x9cslurryxe2x80x9d. Essentially three independent effects can be distinguished in concrete with silicate additions:
filler effect;
pozzolanic reactions;
improvement of the contact zone between aggregate and
cement matrix.
Microsilicas have very small particle diameters. They are in the region of about 0.1 xcexcm. Owing to this property, they are able to fill the interstices between the cement particles. As a result, the packing density in the cement matrix is significantly increased. Although the particle diameter of the cement used is in the order of  less than 9.5 xcexcm, the microsilica particles are much larger, thus resulting in the filler effect.
The pozzolanic properties of the microsilicas are mainly determined by two properties. Firstly, they have a certain proportion of reactive, amorphous siliceous constituents which react with the calcium hydroxide formed during the hydration of cement. Secondly, they have a large specific surface area on which these reactions can take place.
For the purposes of the present invention, the effect of the microsilica in improving the contact zone between aggregate and cement matrix is not brought to bear, because the suspensions used according to the invention contain no siliceous aggregate.
According to the invention, microsilica is added, for example, in amounts of from 10 to 15% by weight, based on the solids content, to the suspension in the form of a dispersion which consists essentially of 50% by weight of microsilica and 50% by weight of water (slurry).
Superfine cements based on slag sand are particularly advantageous for the suspensions used according to the invention because the superfine cements, owing to their low reactivity, require lower water contents and lower contents of fluidizers and/or flow improvers to achieve low-viscosity properties compared to superfine cements based on portland cement.
Particularly suitable fluidizers or flow improvers are, for example, superfluidizers such as lignosulfonate, naphthalenesulfonate, melaminesulfonate, polycarboxylate, which are known as highly effective dispersants for producing superfine cement suspensions.
To produce the suspensions used according to the invention, use is made, in particular, of the following mixtures:
Superfine cement: from 30 to 100% by mass, in particular from 50 to 80, % by mass;
Fluidizer or flow improver (liquid): from 0.1 to 5% by mass, in particular from 0.5 to 4.0, % by mass;
Fluidizer or flow improver (pulverulent): from 0.1 to 2.5% by mass, in particular from 0.5 to 1.5, % by mass;
Microsilica (slurry): from 0 to 30% by mass, in particular from 5 to 15, % by mass;
Pigments (pulverulent): from 0 to 5% by mass, in particular from 1 to 3, % by mass;
Inert mineral materials: from 0 to 70% by mass, in particular from 10 to 30, % by mass;
Superfine fly ash: from 0 to 50% by mass, in particular from 10 to 30, % by mass;
in each case based on the solids content of the suspension.
The low-viscosity suspensions advantageously have a water/solids ratio of from 0.4 to 0.6. Their consistency, measured as the Marsh outflow time, is from 35 to 75 seconds.
To produce a suspension, the required amount of water is, for example, placed in a mixing vessel. The mixer is then started up and fluidizers or flow improvers are added. The previously weighed out dry materials are subsequently added. The mixture is then mixed further and homogenized.